Process of separating isobutylene from admixture of butene-1 and isobutylene



Oct. 7, 1947. H. E. DRENNAN 2,428,516 PROCESS OF SEPARATINGISOBU'I'YLENE FROM ADMIXTURE OF BU'I'ENE-l AND ISOBUTYLENE Filed Sept.24. 1942 ISOMERIZATION CATALYST CHAMBER I 4 m-ID r INVENTOR H E DRENNANKW. QW

A'lTOR EYS Patented Oct. 7, 1947 PROCESS OF SEPARATING ISOBUTYLENE FROMADMIXTURE ISOBUTYLENE OF BUTENE-l AND Harry E. Drennan, Bartlesville,Okla, assignor to Phillips Petroleum Company, a corporation of DelawareApplication September 24, 1942, Serial No. 459,589

2 Claims.

This invention relates to treatment of hydrocarbon mixtures containingeither butene-l and isobutylene or pentene-l and isopentene (2-methyl-butene-l, sometime designated as unsymmetricalmethylethylethylene) in order to separate the isoolefin content of themixture in a form essentially free from the l-olefin.

This application is a continuation-in-part of my prior and copendingapplications Serial Nos. 358,734, filed September 27, 1940, now PatentNo. 2,361,612, issued October 31, 1944, 359,159 filed September 30,1940, and 359,967, filed October 5, 1940, the latter now Patent No.2,298,931, issued October 13, 1942.

In various hydrocarbon conversion processes, particularly cracking,dehydrogenation, reforming, etc. there are produced hydrocarbon mixturesof various compositions containing both saturated and unsaturatedhydrocarbons. Many of the components of such mixtures are particularlyvaluable, provided they can be concentrated without too great anexpense, for use either as such in the form in which they occur in themixture or for use in the synthesis of other hydrocarbons. However inmany cases it is diflicult to concentrate the desired components of sucha mixture by the usual distillation methods without expensive specialequipment. Frequently separation by fractional distillation is whollyimpossible because of the closeness of the boiling points, the formationof azeotropes, etc. Accordingly it is frequently necessary to resort toexpensive and complex solvent extraction, azeotropic distillation, orchemical separation methods.

For example, the dehydrogenation of a mixture consisting primarilyofbutanes will give butene-l, butene-Z, isobutylene, etc. Isobutylene isparticularly valuable for use in the manufacture of synthetic resins andrubber and in the synthesis of isooctane. Butene-l and its isomerbutane-2 are valuable for use in the production of various organiccompounds, one of these being butadiene which is used in the manufactureof synthetic rubber. However the butenes must be individually isolatedfrom the mixture in which they occur in order to be used for thepurposes mentioned. The usual procedure is to concentrate the butenesand then isolate the individual butenes from the concentrate. Theconcentrate is easily prepared by fractional distillation, and butene-2is easily separated from the concentrate by the same method, but theseparation of butene-l and isobutylene by fractional 2 distillation isdifficult and expensive because of their nearly equal volatilitycharacteristics. The boiling points of isobutylene and butene-l are--6.6 C. and 6.1 C. respectively.

Similarly the separation of pentene-l from isopentene by fractionaldistillation is diflicult since their boiling points are 302 C. and 31.1C. respectively. Whereas the boiling points of isobutylene and butene-lare separated by only onehalf of a, degree centigrade, pentene-l andisopentene differ by 0.9 C. While the separation of pentene-l andisopentene may be somewhat less difficult and less commerciallyimportant at the present time, nevertheless the problem is sufficientlyimportant to make a simple solution of considerable value since thesepentenes are valuable chemical intermediates and starting materials forexample in the preparation of piperylene and isoprene which are employedin the manufacture of synthetic rubber.

The principal object of the present invention is to provide an improvedprocess for the separation of C4 or C5 isoolefins from the correspondingl-olefins. Another object is to provide such a process for theseparation of isobutylene from butene-l. Another object is to providesuch a process for the separation of isopentene from pentene-l. Anotherobject is to provide a process accomplishing the foregoing objects whichdoes not employ azeotropic distillation, solvent extraction methods ofseparation, or separations dependent upon formation of a complex oraddition compound of an extraneous chemical which reacts with one of thecomponents sought to be separated. Numerous other objects will morefully hereinafter appear.

The invention may be more easily understood by reference to theaccompanying drawing which portrays diagrammatically one arrangement ofapparatus that has been found suitable for carrying out the process ofthe present invention.

I have discovered that isobutylene may be separated in a verysatisfactory, less expensive way from hydrocarbon mixtures containingthe same and butene-l, by subjecting the mixture to treatment toisomerize the butene-l to its less volatile isomer butene-Z whichpermits the ready recovery by fractional distillation of isobutylene asan overhead product and butane-2 as a kettle product.

The isomerization of the butene-l to butene-2 may be effected in anysuitable manner, for example, by the method of Runge 1,914,674. Howeverit is preferred to use low temperature meth ods examples of which areset forth in my copendin applications above-identified. Thus in myapplication Serial No. 358,734 (Patent No. 2,361,612) the isomerizationis conducted in the vapor phase at above 200 F. over a. catalystcomprising a porous carrier impregnated with a mixture of phosphoruspentoxide and a high melting point tar and heated to carbonizationtemperature before use. In Serial No. 359,159 (Patent No. 2,330,115) theisomerization is carried out at above 150 F. by means of bauxite treatedwith sulfuric or phosphoric acid. In Serial No. 359,967 (Patent No.2,298,931) the isomerization is effected at above 150 F. with a solidcatalyst made by reacting copper oxide with sulfuric or phosphoric acid.Any of these methods may be used. Instead of the foregoing methods, anyother methods may be employed which effect isomerization of the l-olefinto the 2- olefin without substantially affecting the isoolefin or anyother hydrocarbons present. Examples of such other methods are thoseshown in copending application of Hillyer and Schulze Serial No.359,948, filed October 5, 1940, which is directed to isomerization at200 to 600 F. over an adsorbent carrier such as silica gel impregnatedwith sulfuric or phosphoric acid, Hillyer Serial No. 372,921, filedJanuary 2, 1941, Patent No. 2,387,- 994 and drawn to isomerization overan inert carrier impregnated with sulfuric or phosphoric acid, theolefin feed carrying water vapor, Matuszak Serial No. 441,705, filed May4, 1942 (Patent No. 2,403,671), on isomerization over black chromiumoxide, my application Serial No. 446,771, filed June 12, 1942, PatentNo. 2,361,613, on isomerization with anhydrous magnesium oxide, and myapplication Serial No. 450,797, filed July 13, 1942 (Patent No.2,353,552), on effecting the isomerization of anhyrous l-olefins to2-olefins over a solid catalyst which has previously been heated to atemperature above the isomerization temperature to free it from waterand undesirable gases.

I prefer to use such an isomerization process and conditions that atleast 90 per cent of the normal butenes in the isomerization feed appearas butane-2 in the isomerization effluent. I also prefer to so carry outthe isomerization that this lsomerization reaction is substantially thesole reaction taking place and that virtually no other reactions occur,so that the isobutylene and other components of the feed are unaffectedand so that essentially no polymerization, cracking, etc., take place.

I prefer to carry out the isomerization by passing the hydrocarbons overcalcined brucite at temperatures ranging from 200 to 400 F. in the caseof butenes and 200 to 600 F. in the case of pentenes.

Butane-1 and butene-2 can be reversibly isomerized under properconditions of temperature and pressure and preferably in the presence ofsuitable catalysts. The equation for the reaction is as follows:

at comparatively low temperatures, namely 100 C. (212 F.) and lower,this reaction tends to reach equilibrium at about 90 to 95 per centbutene-2 and 5 to per cent butane-1. Higher temperatures tend to shiftthe equilibrium towards butene-l so that at about 400 C. (752 F.) theequilibrium is about 25 per cent butene-l and 75 per cent butene-2. Theboiling points of 4 butenes-2 are 1.0 C. (38.8 F.) and 3.7 C. (38.7 F.)for the cis and trans forms respectively, both of which havesubstantially higher boiling points than either isobutylene or butene-lso that the butenes-2 are readily separated by fractional distillation.

In the process of my invention, I take advantage of the fact thatbutene-l, which boils at nearly the same temperature as isobutylene, canbe readily isomerized to butene-2 which boils at a substantially highertemperature than isobutylene. I apply an isomerization treatment to ahydrocarbon mixture containing isobutylene and butene-1 to convert mostof the butene-l to butene-2 in order to make possible the recovery ofcomparatively pure isobutylene and butene-2 by subjecting theisomerization effluent to fractional distillation. In most cases, Iprefer to use calcined brucite (magnesium hydroxide) as theisomerization catalyst because it is readily available, inexpensive andwill give conversion yields of butene-l to butene-2 up to per cent andbetter when used under proper conditions of temperature and pressure.

Referring to the drawing, a butylene concentrate containing substantialamounts of isobutylene and butene-l is fed via line i and heater 2,which brings the feed to reaction temperature, to isomerization chamber3 maintained at proper temperature and pressure for effectingisomerization of a major proportion or substantially all of the butene-lto butene-2. The isomerization effluent is fed via line 4 and cooler 5into fractionation system 6 which is operated at suitable temperatureand pressure and has a sufficient number of plates to effect completeseparation of isobutylene from butene-2. The isobutylene leaves overheadvia. line I and a suitable proportlon of the condensate is returned tothe tower 6 as reflux while the rest is drawn off as one product vialine 8. The butene-2 is removed via line 9 from the bottom of the tower6 as a kettle roduct.

If desired, either isobutylene or butene-2 of very high purity can beobtained. For example, it pure isobutylene is desired, the isobutylenefraction obtained by fractional distillation may be passed throughanother isomerization catalyst chamber containing calcined brucite. Alarge proportion of the residual butene-l not converted in the firsttreatment will thus be converted to butene-2 which can be fractionatedout as before. This may be repeated as many times as practical or untilthe desired purity of isobutylene is obtained. For example, assumingthat a 50-50 mol mixture of butene-l and isobutylene is to be treated,assuming 90 per cent conversion of butene-l to butene-2 in passing themixture through a calcined brucite catalyst, the residual butane-1 willbe 10 per cent of the original or five mols. In other words, when thismixture is fractionated about 45 mols of butene- 2 will be separatedfrom the mixture leaving an isobutylene-butene-l mixture of about 50 and5 mols, respectively. Or the resultant isobutylene mixture containsabout 9.1 per cent butene-l impurity. Similarly this mixture can betreated to convert a large portion of the residual butene- 1 to butene-2and subsequently fractionated, and so on. The following tabulation givesan approximate indication of the purity of products obtained from a50-50 mol mixture of isobutylene and butene-l assuming 90 per centconversion of butene-l to butene-2 by treating with a calcined severaltimes in succession.

Thus, theoretically, nearly 100 per cent pure isobutylene could be madeif so desired. However, fractionation is not usually controlled thatclosely. Moreover in most cases it probably "would not be practical toemploy more than one or two treatments. Two treatments would leave aresidual of about 1 per cent of butene-l in the isobutylene, and it islikely that the fractionatlon would be so conducted that a small amountof 'butene-2 would be taken overhead with the isobutylene in order toinsure that non-e of the isobutylene was being left in the kettleproducts. Consequently, in commercial operation the resultantisobutylene will be about 97 to 98 per cent pure when the'fe'e'd and thefirst isobutylene fraction are treated and fractionated in succession asdescribed.

As pointed out before, butene-Z of high purity can be obtained by theprocess of my invention. A pure butene-2 fraction can be recovered morereadily than a pure isobutylene fraction, because its volatility isconsiderably less than either isobutylene or butene-l, which permitsrecovering butane-2 as a bottom product of a fractional distillation bysimply taking the isobutylene and butene-l off as an overhead fraction.However, in order to increase the yield of butene-2 as much as possible,it will probably be desirable to subject the mixture to theisomerization steps described in the recovery of isobutylene. In thatcase, a relatively pure isobutylene will be taken off as an overheadproduct and butene-2 will be taken off as a bottom product. If thebutene concentrate fed to the process is practically all butenes, thebutene-2 as recovered will be relatively pure. However, if heavymaterials are present in the feed, another fractionation step will berequired for their removal and the recovery of relatively pure butane-2.

Once butene-2 has been separated from the isobutylene, it may, ifdesired, be isomerized in known manner back to a mixture of butene-l andbutene-Z which in turn may be fractionated to recover butene-l.

The isomerization step may be conducted in either the vapor or liquidphase. However when the isomerization over calcined brucite is conductedin the vapor phase, there is the possibility that a certain amount ofpolymerization will ocour in the catalyst chamber and the polymer, beinga heavy and comparatively non-volatile product, may cover the catalystand render it inefiective. Also, higher temperatures are generally usedin vapor phase treatment than in liquid phase conversion, which areundesirable in that they shift the equilibrium for butene-l and butene-2towards butene-l making 90 per cent or greater conversion impossible. Inthe liquid phase operation the temperature may be only 100 C. (212 F.)or less and the pressure need be only that; required to keep thecomponents in the liquid phase which in most cases will be about 200pounds per square inch gage. Under these conditioris, up to per cent andbetter conversions of bute'ne-l to butene-2 arepo'ssible and any polymerformed tends to be dissolved and washed off of the catalyst and carriedaway by the liquid feed and conversion products as fast as it is formed.Any such polymer is retained in the kettle products of thesubsequentdistillation step or steps.

It will be understood that the feed mixture neednot be a butyleneconcentrate since the process of the invention can be equally wellpracticed on any mixed hydrocarbon feed of six or fewer carbon atoms permolecule and containing substantial quantities if isobutylene andbutene-l. Other 04 hydrocarbons may be present such as normal butane orisobutane, butadiene, vinylacetylene, etc. If the feed containsbu'tene-Z in amount equal to or in excess of the equilibrium value forbute'ne-l and butene-Z in the isomerization step, it will be necessaryof course to preliminarily fractionate to separate the butene-2. In factwherever butene-2 is present in any substantial amounts in the feed itmay be desirable to preliminarily remove all or substantially all of itin order that maximum conversion of butene-l to butene-2 may be attainedin the isomerization step.

While the foregoing discussion relates to separation of isobutylene frombutene-l, it is equally applicable to separation of isopentene frompentene-l by isomerizing the pentene-i to pentene-2 which boils at 35.8and-37.6" C., or, at the least 4.7" C. above isopentene andstill furtherabove pente'ne-l. Separation of pentene-l from lsopentene is frequentlya matter of extreme importance and the present invention makes thisseparation possible without resort to expensive solvent extraction,chemical processes involving formation of addition compounds, orazeotropic distillation. It is therefore to be understood that theforegoing discussion, wherever the context permits, may be read withsubstitution of isopentene for isobutylene, pentene-l for butene-l, andpentene-2 for butene-2.

Example A synthetic mixture of isobutylene and butene-l in theproportion of 50 mols of isobutylene and 50 mols of butene-l wassubjected to isomerization treatment by passage in liquid phase througha converter filled with calcined brucite and maintained at C., thepressure being; sufficiently high to keep the hydrocarbons in.

liquid phase throughout the conversion zone.

The eilluent consisted of isobutylene, butene-2 and. butene-l in theproportions of 50 mols, 45 mols:

and 5 mols, respectively. This product was fractionated in an 80 platecolumn at a top temperature of about F., a pressure of 85 pounds persquare inch absolute, and a reflux ratio of nine to one based on theoverhead. The overhead and kettle products analyzed as follows:

An isomerization treatment on the overhead product and a subsequentfractionation under essentially the same conditions as before gave anisobutylene overhead product of between 96 and 97 mol per cent purity.

From the foregoingit will be seen that the process of my inventionpresents agreat many advantages over previous methods of separatingisobutylene from butene-l or isopentene from pentene-l. is moreeconomically and efiicaciously efiected, and a cleaner separation isattained, with none of the disadvantages attending separation by solventextraction, chemical compound formation, azeotropic distillation andother previously proposed methods. Another advantage is that essentiallypure isobutylene and butene-2 fractions are easily produced which isoften desirable Where isobutylene is to be used as a poly feed or analkylation agent and where butane-2 is to be converted under optimumconditions to butadiene by dehydrogenation. Numerous other advantageswill be apparent to those skilled in the art.

It will be obvious that many modifications other -than those describedin the foregoing may be "practiced without departing from the spirit ofthis invention; consequently, the (foregoing disclosure is not to beconstrued as limiting the invention which is to be taken as limited onlyby the terms and the spirit of the appended claims.

I claim:

1. The process of separating isobutylene from admixture with butene-lwhich comprises passing a liquid mixture of butene-l and isobutyleneover calcined brucite as an isomerization catalyst in a reaction zonemaintained at a temperature of from 200 to 400 F. and under a pressuresufficient to maintain liquid phase throughout the conversion zone andthereby effecting at least 90 per cent conversion of butene-l tobutene-2 as the principal reaction, polymerization occurring to a slightextent, removing the liquid conversion products from the reaction Amongthese are that the separation 8 zone, thereby dissolving the polymerformed, washing same off the catalyst and carrying same away by theliquid feed and conversion products as fast as said polymer is formed,and fractionally distilling the conversion products to separate thebutene-2 irom the isobutyleiie.

2. The process of separating isobutylene from admixture with butene=-1which comprises passing a liquid mixture of blitene-l' and lsobutyleneover calcined hrucite as an isomerization catalyst in a reaction zonemaintained at a temperature of 212 F. and under a pressure suflicient tomaintain liquid phase throughout the conversion zone and therebyefi'ecting at least per cent conversion of butene-l to butene-2 as theprincipal reaction, polymerization occurring to a slight extent,removing the liquid conversion products (from the reaction zone, therebydissolving the polymer form, washing same on the catalyst and carryingsame away by the liquid feed and conversion products as fast as saidpolymer is formed, and fractionally distilling the conversion productsto separate the butane-2 from the isobutylene.

HARRY E. DREN'NAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,914,674 Runge June 20, 19332,199,133 Marschner Apr. 30, 1940 2,281,804 Ruthrufi' May 5, 19422,311,096 Strawn Feb. 16, 1943 2,282,231 Mattox May 5, 1942 2,388,510Voge Nov. 6, 1945 Certificate of Correction Patent No. 2,428,516.October 7, 1947. HARRY E. DRENNAN It is hereby certified that errorsappear in the printed specification of the above numbered patentrequiring correction as follows: Column 4, line 1, for (388 F.) read(338 F.) column 6, line 14, for uantities if read quantities of; column8, line 19, for form read formed and that t c said Letters Patent shouldbe read with these corrections therein that t e same may conform to therecord of the case in the Patent Oflice.

Signed and sealed this 27th day of January, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommiuioner of Patents.

